Convergence apparatus utilizing independently adjustable half-period triangular waveforms

ABSTRACT

A convergence system with minimized control interaction is disclosed. A signal with a parabolic waveform is generated and summed with a signal with a triangular waveform to provide a convergence signal. The triangular waveform has independently adjustable half-periods so that independent top and bottom or right and left adjustment is obtained.

United States Patent 1191 Rhee 1 51 Jan. 2, 1973 s41 CONVERGENCEAPPARATUS 3,543,080 11/1970 Wuensch .315/21 on UTILIZING INDEPENDENTLY3,155,873 ll/l964 Paschal 315/21 TD ADJUSTABLE HALF-PERIOD TRIANGULARWAVEFORMS Inventor:

Assignee:

Filed:

Appl. No.:

U.S.Cl

Int.Cl.

Dong Woo Rhee, Williamsville, NY.

GTE Sylvania Incorporated, Seneca Falls, NY.

April 21, 1971 Field of Search ..3l5/l3 C, 24, 30

References Cited UNITED STATES PATENTS Primary Examiner-Carl D.Quarforth Assistant Examiner-P. A. Nelson Attorney-Norman .l. O'Malley,Robert E. Walrath and Thomas H. Buffton 57] ABSTRACT A convergencesystem with minimized control interaction is disclosed. A signal with aparabolic waveform is generated and summed with a signal with atriangular waveform to provide a convergence signal. The triangularwaveform has independently adjustable halfperiods so that independenttop and bottom or right and left adjustment is obtained.

18 Claims, 10 Drawing Figures PATENTED A 2 7 3. 7 08,715

sum 1 ur 3 G G 132 R i l 7% f 54' H RF, IF Au D10, LUMINANCE cuzommANCE,

AND CON TROL SECTIONS HORIZONTAL 'DEFLECTION APPARATUS CONVERGENCE,

CIRCUImY l31 VERTICAL V INVENTOR. OSCILLATOR m'pu'r 0N6- w. RHEE.

BY P 1 9. l I.

ATTORN E.Y

PATENTEDJAH 2 I975 SHEET 2 [IF 3 iizuuut 3.

luhkjan 2: ZmdUmEH ATTORNE Y PATENTEDJAN 21975 SHEET 3 [IF 3 ATTORNEYCONVERGENCE APPARATUS UTILIZING INDEPENDENTLY ADJUSTABLE HALF-PERIODTRIANGULAR WAVEFORMS CROSS-REFERENCE TO RELATED APPLICATION Dong W.Rhee, Current Drive Deflection Apparatus," Ser. No. 44,476, filed June8, 1970, and assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION This invention relates to convergenceapparatus of the type used to converge the electron beams in a colorcathode ray tube. In a typical color CRT the electron beams arestatically converged at the center of the display screen. Away from thecenter of the screen, however, the beams converge at a point before theyreach the screen. The non-linearity of the beam deflection with respectto the screen is generally spherical requiring a parabolic correctiontoward the edges. This parabolic correction is obtained by applyingparabolic currents of the form i=kt to windings of a deflection yokewhich operate to correct the deflection of the various beams to convergethem at the screen.

Since the amount of correction required varies, the amplitudes of theparabolic currents must be variable. In prior art convergence systemsthe variable amplitudes are obtained by summing sawtooth signals withparabolic signals. Typically, two sawtooth signals with opposite slopesand variable amplitudes are summed with a parabolic signal. One of thesawtooth signals has the greatest effect on one area of the screen,e.g., top or right, while the other sawtooth signal has the greatesteffect on another area of the screen, e.g., bottom or left. The effectsof the two sawtooth signals, however, are not independent. For example,the signal that has the most effect on convergence at the top of thescreen also interacts with or affects the convergence at the bottom ofthe screen and vice versa. Similar interaction occurs between the leftand right convergence signals. Thus, converging the electron beams in acolor CRT in accordance with the prior art is a laborious and timeconsuming procedure because the various controls must be adjusted andreadjusted many times.

Furthermore, distortion of the parabolic signals by the sawtooth signalsmay also disturb or affect the areas of the screen that are staticallyconverted. The distortion may also make it extremely difficult to obtainacceptable convergence on all areas of the screen. This problem oftenresults in a best compromise convergence. The above noted problems areespecially severe in color CRTs with wide'angle deflection becausemisconvergence becomes inherently greater with increasing deflectionangle of the electron beams.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of thisinvention to obviate the above noted disadvantages of the prior art.

It is a further object of this invention to provide improved convergenceapparatus for color CRTs.

It is a further object of this invention to provide a convergenceapparatus with minimized interaction between the signals and controlsapplicable to convergence on different portions of the screen.

The above objects and advantages are achieved in one aspect of thisinvention in a color television receiver having a cathode ray displaytube with a plurality of electron beams therein, a deflection yoke fordeflecting the plurality of electron beams, and convergence apparatusfor converging the electron beams. The convergence apparatus includes aconvergence yoke adapted for mounting in operable relationship with thecathode ray display tube and has a plurality of windings for deflectingcorresponding ones of the plurality of electron beams. A periodic signalwith a parabolic waveform having first and second halfperiods is summedwith one or two periodic signals having triangular waveforms in timecoincidence with the first and second half-periods of the first periodicsignal. The amplitudes of the triangular waveforms are variable. Thesummed signal is a control signal utilized to control a current throughone of the windings of the convergence yoke.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of a colortelevision receiver illustrating the relationship of convergenceapparatus thereto;

FIG. 2 is a waveform diagram illustrating typical prior art convergencewaveforms;

FIG. 3 is a block diagram of one embodiment of the invention;

FIG. 4 is a waveform diagram illustrating typical waveforms used in theinvention;

FIGS. 5A, 5B, 5C, 5D, and 5E are schematic diagrams illustratingelectron beam movement for convergence; and

FIG. 6 is a schematic diagram of one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION For a better understanding of thepresent invention, together with other and further objects, advantagesand capabilities thereof, reference is made to the following disclosureand appended claims in connection with the above-described drawings.

A typical color television receiver is illustrated in FIG. 1. An antenna10 intercepts transmitted signals and conducts them to a block 11 whichcontains the usual RF, IF, audio, luminance, chrominance, and controlsections of a color television receiver. Outputs from the luminance andchrominance sections are applied to a cathode ray display tube 12.Outputs from the control section are applied to a vertical oscillator 13and to a horizontal deflection apparatus 14 which has an outputconnected to a horizontal deflection winding of a deflection yoke 15positioned about the neck of tube 12. Vertical oscillator 13 has anoutput connected to a vertical output stage 16 which has an outputconnected to a vertical deflection winding of deflection yoke I5.Outputs from horizontal deflection apparatus 14 and vertical outputstage 16 are connected to convergence circuitry 17 which has outputsconnected to a convergence yoke 20 positioned or mounted about the neckof tube 12.

Vertical oscillator 13 and vertical output stage 16 are preferably inaccordance with the above-referenced copending application. Horizontaldeflection apparatus 14 can also be in accordance with the referencedapplication.

In a typical prior art convergence system a signal with a parabolicwaveform such as waveform 21 of FIG. 2, is used for convergence. Sincethe magnitude of the error of the electron beams varies, the magnitudeof the correction signal applied to the windings of the convergence yokeshould be variable. The usual prior art technique for varying theamplitude of the signal is to add variable amplitude signals withsawtooth waveforms to the parabolic signal.

Assume a signal with waveform 21 is used to converge the electron beamsat the top and bottom of the screen. A signal with a sawtooth waveformsuch as waveform 22 is added to the parabolic signal to effectconvergence at the bottom of the screen. Another signal with a sawtoothwaveform but having a slope opposite to the slope of waveform 22, isused to effect convergence at the top of the screen. Both sawtoothwaveforms have variable amplitudes so that the correct amount ofconvergence can be obtained.

Waveform 23 is the sum of waveforms 21 and 22. During the vertical scansof the top portion of the screen, the control signal is represented byhalf-periods 24 of waveform 23. After the vertical scans pass thecentral portion of the screen the control signal is represented byhalf-periods 25 of waveform 23.

Ideally, the sawtooth signal represented by waveform 22 should affectthe control signal only during halfperiods 25 since the sawtooth signalis intended for convergence at the bottom of the screen. However, thecontrol signal is also affected or distorted during halfperiods 24 bythe sawtooth signal, thereby affecting or distorting the convergence atthe top of the screen. The second sawtooth signal (not shown) is addedto the signal represented by waveform 23 to form a control signal forapplication to one of the convergence windings. The second sawtoothsignal has its major effect on half-periods 24, however, it also affectshalfperiods 25. Thus, there is control interaction since varying eitherof the sawtooth signals affects the convergence at both the top andbottom of the screen although the effect is greater on one than theother. Similarly, there is control interaction between the controls forleft and right convergence.

In FIG. 3 a block diagram of the invention is shown. Signal generators26 and 27 for generating periodic signals with sawtooth or triangularwaveforms have first outputs connected to variable attenuators 30 and32, respectively, and second outputs connected to variable attenuators31 and 33, respectively. Attenuators 32 and 33 each have an outputconnected to a summing means 34. A signal generator 35 for generating aperiodic signal with a parabolic waveform has an output connected tosumming means 34 which provides a control signal to a convergencewinding 36 of a convergence yoke.

An output of variable attenuator 30 is connected to a differentialsplitter 37 which has a first output connected to a summing means 40anda second output connected to a summing means 41. An output ofvariable attenuator 31 is connected to a differential splitter 42 whichhas first and second outputs connected to summing means 40 and 41,respectively. The output of parabolic signal generator 35 is connectedto summing means 40 and 41. Summing means 40 has an output connected toa convergence winding 43, and summing means 41 has an output connectedto a convergence winding 44. Preferably, convergence windings 36, 43,and 44 are all part of the same convergence yoke.

Parabolic signal generator 35 generates a periodic signal with aparabolic waveform represented by waveform 45 of FIG. 4. Waveform 45 hasfirst-half periods 46 and second half-periods 47. Sawtooth signalgenerators 26 and 27 generate periodic signals with sawtooth ortriangular waveforms represented by waveforms 50 and 51, respectively.Waveform 50 is in time coincidence with the first half-periods 46 ofparabolic waveform 45 while waveform 51 is in time coincidence with thesecond half-periods 47 of parabolic waveform 45.

In typical prior art convergence systems the red and green electronbeams are converged and the blue electron beam is then superimposed.Accordingly, the invention will be explained using this convergenceprocedure, but those skilled in the art will realize that otherprocedures can be used as well.

To converge the beams at the top and bottom of the screen parabolic andsawtooth signals at the vertical deflection frequency are used. Toconverge the beams at the right and left of the screen parabolic andsawtooth signals at the horizontal deflection frequency are used. Thecircuits utilizing vertical and horizontal frequency signals arepreferably independent. Accordingly, to explain convergence at the topand bottom of the screen, assume the frequency of the signals providedby signal generators 26, 27, and 35 are at the vertical frequency.

Assume that the position of the red, green, and blue electron beams atthe top of the screen is that represented by the dots labeled R, G, andB respectively, in FIG. 5A. Sawtooth generator 26 provides a signal withtriangular waveform 50 which is coupled through variable attenuator 30and differential splitter 37 to summing means 40 and 41. In summingmeans 40 and 41 the parabolic and sawtooth signals are summed or addedand applied to convergence windings 43 and 44 which, for example,deflect the red and green electron beams, respectively. The amplitude ofthe sawtooth signal is varied by attenuator 30 to control the amount ofdeflection of the red and green electron beams. The amount of deflectionof each bearn will be equal, assuming that differential splitter 37 isset to provide equal signals to summing means 40 and 41 as isillustrated in FIG. 5A where the R and G beams converge at point 52.

The signal from sawtooth generator 26 is also coupled through variableattenuator 32 to summing means 34 where it is summed with the parabolicsignal from generator 35 and is applied to convergence winding 36 whichdeflects the blue electron beam. Attenuator 32 varies the amplitude ofthe signal therethrough to con verge the blue electron beam of B beam inFIG. 5A to point 52. The blue electron beam can be moved to the left orright, if necessary, by the usual blue lateral magnet.

In FIG. 5B the R and G beams are illustrated oflset in the horizontalplane as well as the vertical plane. Variable attenuator 30 varies theamplitude of the signal therethrough to converge the R and G beams to avertical line 53, however, the beams still are not converged.Differential splitter 37 is varied to decrease the signal to summingmeans 40 while simultaneously increasing the signal to summing means 41.Thus, the R beam is deflected less by winding 43 while the G beam isdeflected more by winding 44, as is shown in FIG. SC, to converge the Rand G beams at point 54. The B beam is converged as was explained above.Thus, variable attenuator 30 causes the R and G beams to converge on avertical line while differential splitter 37 causes the R and G beams toconverge on a horizontal line.

As the electron beams are deflected toward the center of the screen bythe vertical winding of the deflection yoke, the parabolic signal fromgenerator 35 and the sawtooth signal from generator 26 decrease towardzero. After the beams pass the center of the screen, triangular waveform50 remains at zero and the sawtooth signal from generator 27 starts toincrease as shown by triangular waveform 51. Variable attenuators 31 and33 and differential splitter 42 operate on the sawtooth signal toconverge the R, G, and B beams at the bottom of the screen in a mannersimilar to that described above. Variable attenuator 31 converges the Rand G beams on a vertical line while differential splitter 42 convergesthem on a horizontal line. Variable attenuator 33 converges the B beamto the R and G beams.

The convergence of the R, G, and B beams at the right and left of thescreen is similar to that described above and similar circuitry can beused. Assume that generators 26, 27, and 35 provide signals withwaveforms 50, 51, and 45 respectively, at the horizontal scan frequency.The sawtooth signal from generator 26 (triangular waveform 50) iscoupled through variable attenuator 30 and differential splitter 37 tosumming means .40 and 41 where it is summed with the parabolic signalfrom generator 35 and applied to windings 43 and 44. By adjustingattenuator 30 the R and G beams are converged on a horizontal line as isillustrated in FIG. 5D. Adjusting splitter 37 converges the R and Gbeams on a vertical line as is illustrated in FIG. 5E. The signal fromgenerator 36 is also coupled through attenuator 32 to converge the Bbeam. Thus, the signal from generator 36 is used to converge the R, G,and B beams at one side of the screen. Similarly, the signal fromgenerator 27 is used to converge the beams at the other side of thescreen.

From the above description it is clear that similar circuits (butoperating at different frequencies) can be used for top-bottomconvergence and for right-left convergence. However, the circuit of FIG.3 can be used for one convergence circuit (e.g., top-bottom convergence)while a prior art circuit is used for the other circuit (e.g.,right-left convergence), if desired.

In FIG. 6 a specific example of a circuit in accordance with theinvention is illustrated. A source of positive potential illustrated asa terminal 60 is connected to a collector of an NPN transistor 61 whichhas an emitter connected to an emitter of a PNP transistor 62. Thecollector of transistor 62 is connected by a resistor 63 to a commonconductor illustrated as ground. Source 60 is further connected to aconstant current generator 68. A variable current generator 64 isconnected between the base of transistor 62 and ground. The base oftranSistor 61 is connected to the base of transistor 62 by seriesconnected diodes 65 and 66. The

current through variable current generator 64 is varied by a signalapplied at a terminal 67 such as can be provided by vertical oscillator13 of FIG. 1. Components -68 comprise vertical output stage 16. Adescription of the operation and of various alternative forms ofvertical output stage 16 can be found in the abovereferenced copendingapplication.

The junction of the emitters of transistors 61 and 62 is connected toone end of a vertical deflection winding 70 of the deflection yoke, theother end of which is connected by a coupling capacitor 71 in serieswith a resistor 72 to ground. The junction between resistor 72 andcapacitor 71 is connected by a resistor 73 in series with a resistor 74to the junction between the collector of transistor 62 and resistor 63.Resistors 63 and 72 are preferably very small. The junction betweenresistors 73 and 74. is connected by a diode 75 to one end of theresistance element of each of potentiometers 76 and 77, the other endsof which are connected to ground. The wiper of potentiometer 77 isconnected to the wiper of a potentiometer 80.

The junction between the collector of transistor 62 and resistor 63 isconnected by a resistor 81 in series with a diode 82 to one end of theresistance element of each of potentiometers 83 and 84, the other endsof which are connected to ground. The wiper of potentiometer 84 isconnected to the wiper of a potentiometer 85.

One end of the resistance element of potentiometer 85 is connected by aresistor 86 in series with a resistor 87 to one end of the resistanceelement of potentiometer 80. The junction between resistors 86 and 87 isconnected to ground by a resistor 90 and is further connected by aresistor 91 to a control electrode ofa control means illustrated as thebase of a transistor 92. The emitter of transistor 92 is connected toground by a resistor 93. An output electrode or collector of transistor92 is connected by a convergence winding 94, such as the convergencewinding for the red electron beam, to a source of positive potentialillustrated as a terminal 95. A damping resistor 96 can be connected inparallel with winding 94 if necessary, and winding 94 can be a splitwinding as illustrated.

The other end of the resistance element of potentiometer 85 is connectedby a resistor 100 in series with a resistor 10] to the other end of theresistance element of potentiometer 80. The junction between resistors100 and 101 is connected to ground by a resistor 102 and by a resistor103 to a control electrode of a control means illustrated as the base ofa transistor 104. The emitter of transistor 104 is connected to groundby a resistor 105. An output electrode or collector of transistor 104 isconnected by a convergence winding 106, such as the convergence windingfor the green electron beam, to source 95. A damping resistor 107 can beconnected in parallel with winding 106 if necessary, and winding 106 canbe a split winding as illustrated.

The wiper of potentiometer 83 is connected by a resistor 110 in serieswith a resistor 111 to the wiper of potentiometer 76. The junctionbetween resistors 110 and 111 is connected to ground by a resistor 112and by a resistor 113 to a control electrode of a control meanSillustrated as the base of a transistor 114. The emitter of transistor114 is connected to ground by a resistor 115. An output electrode orcollector of transistor 114 is connected by a convergence winding 116,such as the convergence winding for the blue electron beam, to source95. A damping resistor 117 can be connected in parallel with winding 116if necessary, and winding 116 can be a split winding as illustrated.

The junction between deflection winding 70 and the emitters oftransistor 61 and 62 is connected to an input of an integrator 120illustrated as a resistor and capacitor connected in an RC circuit. Theoutput of integrator 120 is connected by a coupling capacitor 121 inseries with a resistor 122 to the base of transistor 92 which is furtherconnected to ground by a resistor 123. The junction between capacitor121 and resistor 122 is connected by a reverse poled diode 124 to asource of positive potential illustrated as a terminal 125. Source 125and diode 124 act as a clamping circuit. The junction of capacitor 121and resistor 122 is further connected by a resistor 126 to the base oftransistor 104 and by a resistor 127 to the base of transistor 114. Thebase of transistor 104 is further connected to ground by a resistor 130.The base of transistor 114 is further connected to ground by a resistor131.

In operation, transistors 61 and 62 provide a sawtooth current throughdeflection winding 70. A large portion of the voltage developed acrossthe winding 70 due to this sawtooth current is integrated by integrator120 to provide a periodic signal with a parabolic waveform illustratedby waveform 45 of FIG. 4. The sawtooth deflection current also flowsthrough resistor 72 to provide a sawtooth voltage thereacrossillustrated as waveform 132 of FIG. 4. As was explained in theabove-referenced copending application, transistor 62 conducts currentonly during one-half of the cycle of the sawtooth deflection current.Thus, the voltage across resistor 63 is represented by waveform 50 ofFIG. 4. This signal is coupled through resistor 81 and diode 82 to theresistance elements of potentiometers 83 and 84. The voltages acrossresistors 63 and 72 are summed by resistors 73 and 74. The summedvoltage, represented by waveform 51 of FIG. 4 which is the sum ofwaveforms 50 and 132, is coupled by diode 75 to the resistance elementsof potentiometers 76 and 77. Thus, the vertical output stage, deflectionwinding 70, integrator 120, and the various resistors correspond togenerators 26, 27, and 35 of FIG. 3.

Potentiometer 84 varies the amplitude of the sawtooth signal representedby waveform 50 and cor responds to variable attenuator 30 of FIG. 3.Potentiometer 85 splits the signal at its wiper into two signals withamplitudes relatively or differentially variable by the wiper ofpotentiometer 85. Thus, potentiometer 85 corresponds to differentialsplitter 37. Potentiometers 77 and 80 operate similar to potentiometers84 and 85 to split the sawtooth signal represented by waveform 51 intotwo variable amplitude signals. Thus, potentiometers 77 and 80correspond to variable attenuator 31 and differential splitter 42,respectively.

One signal from potentiometer 80 is summed with one signal frompotentiometer 85 by resistors 86, 87, and 90 to provide a periodicsignal with a waveform illustrated as waveform 133 of FIG. 4. Thissignal has first and second half-periods each with a triangular waveformin time coincidence with the first and second half-periods of theparabolic signal as is illustrated in FIG. 4. This periodic signal issummed with the parabolic signal by resistors 91, 122, and 123. Thus,resistors 86, 87, 90, 91, 122, and 123 correspond to summing means 40 ofFIG. 3. The control signal formed at the base of transistor 92 controlsthe current through transistor 92 and hence the current through winding94 to deflect the red electron beam.

The other signals provided by potentiometers and are similarly summed byresistors 100, 101, and 102. The resultant signal is summed with theparabolic signal by resistors 103, 126, and to provide a control signalto control the current through transistor I04 and winding 106 to deflectthe green electron beam. Thus, resistors 100, 101, 102, 103, 126, and130 correspond to summing means 41.

Potentiometers 76 and 83 provide signals with waveforms 51 and 50,respectively, which have variable amplitudes depending upon the positionof the potentiometer wipers. These signals are summed by resistors 110,111, and 112 to provide a periodic signal with a waveform represented,by waveform 133. This signal is summed with the parabolic signal byresistors 113, 127, and 131 to provide a control signal for controllingthe current through transistor 114 and winding 116 to deflect the blueelectron beam. Thus, potentiometers 83 and 76 correspond to variableattenuators 32 and 33, respectively, while the various summing resistorscorrespond to summing means 34.

While the circuit of FIG. 6 has been described with reference to thevertical deflection apparatus, it is clear that a similar circuit can beused with the horizontal deflection apparatus to generate suitableconvergence signals. Alternatively, the horizontal retrace pulse(flyback pulse) can be singly integrated to provide a sawtooth signaland doubly integrated to provide a parabolic signal with suitablesumming circuits used to provide signals in accordance with waveforms 50and 51.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the invention as defined bythe appended claims.

I claim:

1. In a color television receiver having a cathode ray display tube forgenerating a plurality of electron beams therein and a deflection yokefor deflecting said plurality of electron beams, convergence apparatusfor converging the electron beams comprising:

a convergence yoke mounted in operable relationship with said cathoderay display tube and having a plurality of windings for deflectingcorresponding ones of said plurality of electron beams;

first means for generating a first periodic signal with a parabolicwaveform having first and second halfperiods;

second means for generating second and third periodic signals, saidsecond periodic signal having a triangular waveform during said firsthalf-periods and said third periodic signal having a triangular waveformduring said second half-periods, said second and third periodic signalsfurther having independently variable amplitudes;

summing means connected to said first and second means for summing saidfirst, second, and third periodic signals to provide a control signalwith independently variable amplitudes during said first and secondhalf-periods; and

means connecting said summing means to one of said windings of saidconvergence yoke for controlling the current through said one of saidwindings with said control signal.

2. Convergence apparatus as defined in claim 1 including:

third means for generating fourth and fifth periodic signals, saidfourth periodic signal having a triangular waveform during said firsthalf-periods and said fifth periodic signal having a triangular waveformduring said second half-periods, said fourth and fifth periodic signalsfurther having independently variable amplitudes;

second summing means connected to said first and third means for summingsaid first, fourth, and fifth periodic signals to provide a secondcontrol signal with independently variable amplitudes during said firstand second half-periods; and

means connecting said second summing means to a second one of saidwindings of said convergence yoke for controlling the current throughsaid second one of said windings in accordance with said second controlsignal.

3. Convergence apparatus as defined in claim 2 wherein said second andthird means include:

a first signal generator for generating a periodic signal having atriangular waveform during said first half-periods of said firstperiodic signal;

a second signal generator for generating a periodic signal having atriangular waveform during said second half-periods of said firstperiodic signal;

first and second variable resistance means connected to said first andsecond signal generators, respectively, for varying the amplitudes ofthe periodic signals generated by said first and second signalgenerators; and

third and fourth variable resistance means connected to said first andsecond variable resistance means, respectively, said third variableresistance means for providing said second and fourth periodic signalswith relatively variable amplitudes, and said fourth variable resistancemeans for providing said third and fifth periodic signals withrelatively variable amplitudes.

4. Convergence apparatus as defined in claim 2 wherein said meansconnecting said first-named summing means to one of said windingsincludes a first transistor, and said means connecting said secondsumming means to a second one of said windings includes a secondtransistor.

5. Convergence apparatus as defined in claim 2 including:

fourth means for generating sixth and seventh periodic signals, saidsixth periodic signal having a triangular waveform during said firsthalf-periods and said seventh periodic signal having a triangularwaveform during said second half-periods, said sixth and seventhperiodic signals further having independently variable amplitudes;

third summing means connected to said first and fourth means for summingsaid first, sixth, and seventh periodic signals to provide a thirdcontrol signal with independently variable amplitudes during said firstand second half-periods; and

means connecting said third summing means to a third one of saidwindings of said convergence yoke for controlling the current throughsaid third one of said windings in accordance with said third controlsignal.

6. Convergence apparatus as defined in claim 2 wherein said first meansincludes an integrator for integrating a signal representative of acurrent flowing through a winding of said deflection yoke for generatingsaid first periodic signal, and said second and third means generatesaid second and third periodic signals from said current flowing throughsaid winding of said deflection yoke.

7. In a color television receiver having a cathode ray display tube witha plurality of electron beams therein, a deflection yoke for deflectingsaid plurality of electron beams, and a convergence yoke adapted formounting in operable relationship with said cathode ray display tube andhaving a plurality of windings for deflecting corresponding ones of saidplurality of electron beams, a convergence circuit comprising:

first signal generating means for generating a first periodic signalwith a parabolic waveform having first and second half-periods;

second signal generating means for generating second and third periodicsignals each having first and second half-periods in time coincidencewith said first and second half-periods, respectively, of said firstperiodic signal and each further having a first triangular waveform witha variable amplitude during said first half-periods and a secondtriangular waveform with a variable amplitude during said secondhalf-periods;

first summing and control means connected to said first and secondsignal generating means and to a first winding of said convergence yokefor summing said first and second periodic signals to provide a firstcontrol signal for controlling the current through said first winding;and

second summing and control means connected to said first and secondsignal generating means and to a second winding of said convergence yokefor summing said first and third periodic signals to provide a secondcontrol signal for controlling the current through said second winding.

8. A convergence circuit as defined in claim 7 wherein said secondsignal generating means includes first and second signal generators forgenerating signals with said first and second triangular waveforms,respectively, and first and second summing means each connected to saidfirst and second signal generators for summing the signals from saidfirst and second signal generators to provide said second and thirdperiodic signals, respectively.

9. A convergence circuit as defined in claim 8 wherein said first signalgenerator includes a first variable attenuator for varying the amplitudeof the signals generated by said first signal generator and a firstdifferential splitter connected to said first variable attenuator forproviding first and second signals with differentially variableamplitudes to said first and second summing means, respectively, andsaid second signal generator includes a second variable attenuator forvarying the amplitude of the signals generated by said second signalgenerator and a second differential splitter connected to said secondvariable attenuator for providing third and fourth signals withdifferentially variable amplitudes to said first and second summingmeans, respectively.

10. A convergence circuit as defined in claim 9 wherein said first andsecond variable attenuators and said first and second differentialsplitters are each potentiometers.

11. A convergence circuit as defined in claim 7 wherein said first andsecond summing and control means include first and second summing means,respectively, for summing said first and second periodic signals andsaid first and third periodic signals to provide said first and secondcontrol signals, respectively, and first and second transistors,respectively, each havin g a control electrode connected to therespective one of said first and second summing means and an outputelectrode connected to the respective one of said first and secondwindings.

12. A convergence circuit as defined in claim 7 wherein said firstsignal generating means includes an integrator connected to saiddeflection yoke for integrating a voltage across a winding of saiddeflection yoke.

13. A convergence circuit as defined in claim 8 wherein said first andsecond signal generators include means for deriving first and secondvoltages, respectively, from a current flowing through a winding of saiddeflection yoke.

14. A convergence circuit as defined in claim 7 including a third signalgenerating means for generating a fourth periodic signal having firstand second halfperiods in time coincidence with said first and secondhalf-periods, respectively, of said first periodic signal and furtherhaving a first triangular waveform with a variable amplitude during saidfirst half-periods and a second triangular waveform with a variableamplitude during said second half-periods; and third summing and controlmeans connected to said first and third signal generating meansand to athird winding of said convergence yoke for summing said first and fourthperiodic signals to provide a third control signal and for controllingthe current through said third winding. I

15. A convergence circuit as defined in claim 14 wherein said thirdsignal generating means includes a first variable attenuator for varyingthe amplitude of said fourth periodic signal during said firsthalf-periods and a second variable attenuator for varying the amplitudeof said fourth periodic signal during said second half-periods.

16. A convergence circuit as defined in claim 15 wherein said thirdsumming and control means includes summing means for summing said firstand fourth periodic signals to provide said third control signal and atransistor having a control electrode connected to said summing meansand an output electrode connected to said third winding.

17. A convergence circuit as defined in claim 7 wherein the frequency ofsaid first, second, and third periodic signals is at the verticaldeflection frequency of the television receiver.

l A convergence circuit as defined in claim 7 wherein the frequency ofsaid first, second, and third periodic signals is at the horizontaldeflection frequency of the television receiver.

1. In a color television receiver having a cathode ray display tube forgenerating a plurality of electron beams therein and a deflection yokefor deflecting said plurality of electron beams, convergence apparatusfor converging the electron beams comprising: a convergence yoke mountedin operable relationship with said cathode ray display tube and having aplurality of windings for deflecting corresponding ones of saidplurality of electron beams; first means for generating a first periodicsignal with a parabolic waveform having first and second half-periods;second means for generating second and third periodic signals, saidsecond periodic signal having a triangular waveform during said firsthalf-periods and said third periodic signal having a triangular waveformduring said second half-periods, said second and third periodic signalsfurther having independently variable amplitudes; summing meansconnected to said first and second means for summing said first, second,and third periodic signals to provide a control signal withindependently variable amplitudes during said first and secondhalf-periods; and means connecting said summing means to one of saidwindings of said convergence yoke for controlling the current throughsaid one of said windings with said control signal.
 2. Convergenceapparatus as defined in claim 1 including: third means for generatingfourth and fifth periodic signals, said fourth periodic signal having atriangular waveform during said first half-periods and said fifthperiodic signal having a triangular waveform during said secondhalf-periods, said fourth and fifth periodic signals further havingindependentLy variable amplitudes; second summing means connected tosaid first and third means for summing said first, fourth, and fifthperiodic signals to provide a second control signal with independentlyvariable amplitudes during said first and second half-periods; and meansconnecting said second summing means to a second one of said windings ofsaid convergence yoke for controlling the current through said secondone of said windings in accordance with said second control signal. 3.Convergence apparatus as defined in claim 2 wherein said second andthird means include: a first signal generator for generating a periodicsignal having a triangular waveform during said first half-periods ofsaid first periodic signal; a second signal generator for generating aperiodic signal having a triangular waveform during said secondhalf-periods of said first periodic signal; first and second variableresistance means connected to said first and second signal generators,respectively, for varying the amplitudes of the periodic signalsgenerated by said first and second signal generators; and third andfourth variable resistance means connected to said first and secondvariable resistance means, respectively, said third variable resistancemeans for providing said second and fourth periodic signals withrelatively variable amplitudes, and said fourth variable resistancemeans for providing said third and fifth periodic signals withrelatively variable amplitudes.
 4. Convergence apparatus as defined inclaim 2 wherein said means connecting said first-named summing means toone of said windings includes a first transistor, and said meansconnecting said second summing means to a second one of said windingsincludes a second transistor.
 5. Convergence apparatus as defined inclaim 2 including: fourth means for generating sixth and seventhperiodic signals, said sixth periodic signal having a triangularwaveform during said first half-periods and said seventh periodic signalhaving a triangular waveform during said second half-periods, said sixthand seventh periodic signals further having independently variableamplitudes; third summing means connected to said first and fourth meansfor summing said first, sixth, and seventh periodic signals to provide athird control signal with independently variable amplitudes during saidfirst and second half-periods; and means connecting said third summingmeans to a third one of said windings of said convergence yoke forcontrolling the current through said third one of said windings inaccordance with said third control signal.
 6. Convergence apparatus asdefined in claim 2 wherein said first means includes an integrator forintegrating a signal representative of a current flowing through awinding of said deflection yoke for generating said first periodicsignal, and said second and third means generate said second and thirdperiodic signals from said current flowing through said winding of saiddeflection yoke.
 7. In a color television receiver having a cathode raydisplay tube with a plurality of electron beams therein, a deflectionyoke for deflecting said plurality of electron beams, and a convergenceyoke adapted for mounting in operable relationship with said cathode raydisplay tube and having a plurality of windings for deflectingcorresponding ones of said plurality of electron beams, a convergencecircuit comprising: first signal generating means for generating a firstperiodic signal with a parabolic waveform having first and secondhalf-periods; second signal generating means for generating second andthird periodic signals each having first and second half-periods in timecoincidence with said first and second half-periods, respectively, ofsaid first periodic signal and each further having a first triangularwaveform with a variable amplitude during said first half-periods and asecond triangular waveform with a variable amplitude during said secondhalf-periods; FIRST summing and control means connected to said firstand second signal generating means and to a first winding of saidconvergence yoke for summing said first and second periodic signals toprovide a first control signal for controlling the current through saidfirst winding; and second summing and control means connected to saidfirst and second signal generating means and to a second winding of saidconvergence yoke for summing said first and third periodic signals toprovide a second control signal for controlling the current through saidsecond winding.
 8. A convergence circuit as defined in claim 7 whereinsaid second signal generating means includes first and second signalgenerators for generating signals with said first and second triangularwaveforms, respectively, and first and second summing means eachconnected to said first and second signal generators for summing thesignals from said first and second signal generators to provide saidsecond and third periodic signals, respectively.
 9. A convergencecircuit as defined in claim 8 wherein said first signal generatorincludes a first variable attenuator for varying the amplitude of thesignals generated by said first signal generator and a firstdifferential splitter connected to said first variable attenuator forproviding first and second signals with differentially variableamplitudes to said first and second summing means, respectively, andsaid second signal generator includes a second variable attenuator forvarying the amplitude of the signals generated by said second signalgenerator and a second differential splitter connected to said secondvariable attenuator for providing third and fourth signals withdifferentially variable amplitudes to said first and second summingmeans, respectively.
 10. A convergence circuit as defined in claim 9wherein said first and second variable attenuators and said first andsecond differential splitters are each potentiometers.
 11. A convergencecircuit as defined in claim 7 wherein said first and second summing andcontrol means include first and second summing means, respectively, forsumming said first and second periodic signals and said first and thirdperiodic signals to provide said first and second control signals,respectively, and first and second transistors, respectively, eachhaving a control electrode connected to the respective one of said firstand second summing means and an output electrode connected to therespective one of said first and second windings.
 12. A convergencecircuit as defined in claim 7 wherein said first signal generating meansincludes an integrator connected to said deflection yoke for integratinga voltage across a winding of said deflection yoke.
 13. A convergencecircuit as defined in claim 8 wherein said first and second signalgenerators include means for deriving first and second voltages,respectively, from a current flowing through a winding of saiddeflection yoke.
 14. A convergence circuit as defined in claim 7including a third signal generating means for generating a fourthperiodic signal having first and second half-periods in time coincidencewith said first and second half-periods, respectively, of said firstperiodic signal and further having a first triangular waveform with avariable amplitude during said first half-periods and a secondtriangular waveform with a variable amplitude during said secondhalf-periods; and third summing and control means connected to saidfirst and third signal generating means and to a third winding of saidconvergence yoke for summing said first and fourth periodic signals toprovide a third control signal and for controlling the current throughsaid third winding.
 15. A convergence circuit as defined in claim 14wherein said third signal generating means includes a first variableattenuator for varying the amplitude of said fourth periodic signalduring said first half-periods and a second variable attenuator forvarying the amplitude of said fourth periodic Signal during said secondhalf-periods.
 16. A convergence circuit as defined in claim 15 whereinsaid third summing and control means includes summing means for summingsaid first and fourth periodic signals to provide said third controlsignal and a transistor having a control electrode connected to saidsumming means and an output electrode connected to said third winding.17. A convergence circuit as defined in claim 7 wherein the frequency ofsaid first, second, and third periodic signals is at the verticaldeflection frequency of the television receiver.
 18. A convergencecircuit as defined in claim 7 wherein the frequency of said first,second, and third periodic signals is at the horizontal deflectionfrequency of the television receiver.